1. Field of the Invention
The present invention relates to ionomer/polyamide blends with improved flow and impact characteristics and a method of achieving the same. More specifically but not by way of limitation, the present invention relates to the addition of low molecular weight ethylene/acrylic (methacrylic) acid copolymer, very low density polyethylene (VLDPE), ethylene propylene elastomer (EPR), maleic anhydride grafted ethylene propylene elastomer (MAN-g-EPR), maleic anhydride grafted very low density polyethylene (MAN-g-VLDPE) or mixtures thereof to an ionomer/polyamide blend in order to reduce viscosity of such blend and simultaneously maintain or improve low temperature Izod impact.
2. Description of the Related Art
It is generally known in the art to employ a thermoplastic alloy based on a blend of ionomer and high density polyethylene or polyamide for injection molding exterior automotive molded-in-color fascia, bumper covers, side moldings and other decorative trim. These types of polymer blends are disclosed, for example, in U.S. Pat. No. 5,866,658 and are commercially available under the tradename Bexloy(copyright) from E. I. du Pont de Nemours and Company. They involve a copolymer of an xcex1-olefin, typically ethylene, copolymerized with an xcex1,xcex2-ethenically unsaturated carboxylic acid, typically acrylic acid, methacrylic acid or mixtures thereof, wherein the acid copolymer has preferably from 65 to 100 percent of the acid groups neutralized with metal ions such as zinc, sodium or the like. Such ionomers are commercially available under the tradename Surlyn(copyright) from E. I. du Pont de Nemours and Company. In the ""658 patent, the highly neutralized acid copolymer is blended with preferably one or more semicrystalline polyamides such as polycaproamide (nylon 6) and polyhexamethylene adipamide (nylon 6,6). One difficulty with such blends is the achieving and sustaining of optimum rheology without significantly compromising physical properties such as impact resistance and tensile strength.
In view of the above mentioned problem, it has now been discovered that the addition or incorporation of a low molecular weight copolymer of ethylene copolymerized with acrylic acid, methacrylic acid and mixtures thereof optionally in combination with one or more additive such as very low density polyethylene (VLDPE), maleic anhydride grafted VLDPE, ethylene propylene diene monomer (EPDM) rubber, maleic anhydride grafted EPDM, and mixtures thereof improves the flow properties of the resulting ionomer/polyamide blend without significantly degrading physical properties such as impact resistance and tensile strength.
Thus, the present invention provides an ionomer/polyamide blend having improved flow properties comprising for every one hundred parts by weight of ionomer/polyamide blend:
(i) from one to twenty parts by weight low molecular weight copolymer of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures there of, wherein the low molecular weight copolymer has a melt index (ASTM D1238) of greater than 350 dg/min and an acrylic acid and methacrylic acid combined comonomer content of at least 5 weight percent; and optionally
(ii) up to twenty parts per weight of one or more additives selected from the group consisting of very low density polyethylene (VLDPE), maleic anhydride grafted VLDPE, ethylene propylene (EPR) rubber, ethylene propylene diene monomer (EPDM) rubber, maleic anhydride grafted EPR, maleic anhydride grafted EPDM, and mixtures thereof.
The present invention further provides a method of reducing the viscosity of an ionomer/polyamide blend without significantly degrading impact resistance and tensile strength comprising the steps of blending for every one hundred parts by weight of ionomer/polyamide blend
(i) from one to twenty parts by weight low molecular weight copolymer of ethylene and at least one other comonomer selected from the group consisting of acrylic acid, methacrylic acid and mixtures thereof, wherein the low molecular weight copolymer has a melt index (ASTM D1238) of greater than 350 dg/min and an acrylic acid and methacrylic acid combined comonomer content of at least 5 weight percent; and optionally
(ii) up to twenty parts per weight of one or more additives selected from the group consisting of very low density polyethylene (VLDPE), maleic anhydride grafted VLDPE, ethylene propylene (EPR) rubber, ethylene propylene diene monomer (EPDM) rubber, maleic anhydride grafted EPR, maleic anhydride grafted EPDM, and mixtures thereof.
The low molecular weight copolymer has a melt index as low as 350 but preferably a melt index of at least 900 dg/min and an acrylic acid and methacrylic acid combined comonomer content of at least 5 weight percent and preferably 9 weight percent or greater.